Charged particle beam apparatus

ABSTRACT

A charged particle beam device is provided that performs proper beam adjustment while suppressing a decrease in MAM time, with a simple configuration without adding a lens, a sensor, or the like. The charged particle beam device includes: an optical element which adjusts a charged particle beam emitted from a charged particle source; an adjustment element which adjusts an incidence condition of the charged particle beam with respect to the optical element; and a control device which controls the adjustment element, wherein the control device determines a difference between a first feature amount indicating a state of the optical element based on the condition setting of the optical element, and a second feature amount indicating a state where the optical element reaches based on the condition setting and executes adjustment by the adjustment element when the difference is greater than or equal to a predetermined value.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.15/869,460, filed Jan. 12, 2018, which is a continuation of U.S.application Ser. No. 15/292,832, filed Oct. 13, 2016, now issued as U.S.Pat. No. 9,892,887 on Feb. 13, 2018, which claims priority under 35U.S.C. § 119 from Japanese Patent Application No. 2015-203339, filedOct. 15, 2015, the entire disclosures of which are herein expresslyincorporated by reference.

TECHNICAL FIELD

The present invention relates to a charged particle beam device whichobserves, inspects, or measures a fine circuit pattern of asemiconductor device, a liquid crystal, or the like by a chargedparticle beam, and in particular, to a charged particle beam deviceprovided with an adjustment element which adjusts the optical conditionof a charged particle beam.

BACKGROUND ART

According to the miniaturization and complexity of a semiconductordevice, a technique of managing a lithography or etching process byinspecting and measuring a fine pattern of about 10 nm formed on a waferwith a high degree of accuracy and at high speed is widely used insemiconductor plants in the world. In particular, a length measurementscanning electron microscope (Critical Dimension Scanning ElectronMicroscope: CD-SEM) is a measurement device essential to processmanagement of a fine pattern.

In order to perform high-precision measurement by using a device such asthe CD-SEM, a device condition needs to be properly set. In PTL 1, thereis described a technique of determining the necessity of automatic focusadjustment (Auto Focus: AF) on the basis of the evaluation of a powerspectrum high-frequency component of a SEM image. In PTL 2, there isdisclosed a method of determining the necessity of axis adjustment of acharged particle beam on the basis of an image quality evaluation valueof a SEM image. In PTL 3, there is disclosed a method of determining thenecessity of an aberration correction on the basis of the output resultof an environment sensor, or the detection results of the sharpness ofimages captured from a plurality of directions, in a SEM equipped withan aberration corrector. In PTL 4, there is disclosed an electromagneticlens in which it is provided with two coils and it is possible to adjusta focusing condition while making the amount of heat generationconstant, by adjusting the difference between currents flowing throughboth the coils, while making the sum of the currents constant.

CITATION LIST Patent Literature

PTL 1: JP-A-10-333020

PTL 2: JP-A-2010-182424 (corresponding U.S. Pat. No. 8,294,118)

PTL 3: JP-A-2014-135227

PTL 4: JP-A-2009-176542

SUMMARY OF INVENTION Technical Problem

In the CD-SEM which is installed in a mass-production plant for asemiconductor device, very high processing capacity is required, and inparticular, the shortening of the time of movement/imagecapture/measurement (Move Acquire Measure: MAM time) during automaticmeasurement and improvement of wafer processing capacity per unit timeare required. In recent years, in addition to line-width measurement ofa standard line and space (L & S) pattern, measurement of the bottomwidths and side wall shapes of a deep groove and a deep hole has beenfrequently used.

If the setting conditions of an electron beam are changed duringautomatic measurement in order to measure these various measurementtargets, the equilibrium state of an optical element such as anobjective lens collapses from immediately after the switching, wherebythe focus of the electron beam is shifted, and further, there is a casewhere astigmatism or axis shift occurs. It is not possible to evaluatethe discrepancy between a temperature at which the objective lens entersan equilibrium state and the current temperature, and therefore, inorder to perform measurement at proper beam conditions, it is consideredto interrupt the measurement for a sufficient period of time in which adevice is stabilized, or to frequently perform automatic adjustment ofthe beam. However, the measurement interruption or the frequentautomatic adjustment reduces the MAM time.

In particular, in a case of performing a determination of the necessityof adjustment by using the image processing technique and the like asdescribed in PTLs 1 to 3, it is necessary to perform image acquisitionfor the adjustment, or it is necessary to provide a sensor or the likefor determining the necessity of the adjustment. Further, it isdifficult to evaluate deviation from the equilibrium state of theobjective lens by seeing an image or the like, and therefore, it is notpossible to determine a proper adjustment timing which changes accordingto the deviation from the equilibrium state of the objective lens. It isalso conceivable to adjust the amount of current flowing through twocoils in order to adjust a focusing condition, while making the amountof heat generation constant, as described in PTL 4. However, in terms oftwo coils being put in the electromagnetic lens and the two coils beingcontrolled at the same time, application to the device is difficult fromthe aspects of a space and cost.

A charged particle beam device having an object to perform proper beamadjustment while suppressing a decrease in MAM time, with a simpleconfiguration without adding a lens, a sensor, or the like, is proposedbelow.

Solution to Problem

As an aspect for achieving the above object, there is proposed a chargedparticle beam device including: an optical element which adjusts acharged particle beam emitted from a charged particle source; anadjustment element which adjusts an incidence condition of the chargedparticle beam with respect to the optical element; and a control devicewhich controls the adjustment element, in which the control devicedetermines a difference between a first feature amount indicating astate of the optical element based on the condition setting of theoptical element, and a second feature amount indicating a state wherethe optical element reaches based on the condition setting and executesadjustment by the adjustment element when the difference is greater thanor equal to a predetermined value.

Advantageous Effects of Invention

According to the above configuration, both of higher throughput of thedevice and high-precision measurement or inspection based on beamadjustment at a proper timing can be realized.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram showing a basic configuration of a chargedparticle beam device.

FIG. 2 is a flowchart showing a temperature fluctuation trackingprocessing step.

FIG. 3 is a flowchart for describing a threshold value determinationprocessing step during automatic measurement.

FIG. 4 is a list of temperature threshold values with respect to theacceleration, the current, and the depth of focus of an electron beam.

FIGS. 5A-5E are diagrams showing setting examples of a threshold valuedetermination during the automatic measurement in a measurement recipeediting screen.

FIGS. 6A-6C are diagrams showing displacement of the feature amount ofan optical element.

FIG. 7 is an optical condition switching sequence during the automaticmeasurement.

FIG. 8 is a schematic diagram showing a basic configuration of a chargedparticle beam device according to a second example.

FIG. 9 is a flowchart showing a measurement step of a measurement devicestored in a recipe.

DESCRIPTION OF EMBODIMENTS

A temperature fluctuation amount, a magnetic field fluctuation amount, apressure change amount, and the like occurring in a change in setting ofa beam are the feature amounts of an optical element, which act on anoperating status of the optical element through a material property.There is a case where it is possible to calculate the feature amount ofthe optical element from the history of device setting of control valuesof a current, voltage, and the like which control the optical element.For example, a temperature fluctuation amount from an equilibrium statein the setting condition of an electron beam can be calculated based onthe history of device setting of the amount of heat generation of anobjective lens.

Hereinafter, a charged particle beam device having a function ofcarrying out arbitrary automatic adjustment in a case where thetemperature fluctuation amount exceeds an arbitrary threshold value willbe described. By being provided with a monitor device for monitoring atemperature fluctuation amount, it becomes possible to perform automaticadjustment only in a switching condition in which a length measurementvalue fluctuation occurs, and thus it is possible to avoid unnecessaryautomatic adjustment. Accordingly, it is possible to provide a chargedparticle beam device which realizes automatic measurement in which bothof a throughput and high-precision measurement can be achieved.

According to examples which are described below, it is possible toprovide a signal detection method, and a device which instantly changesthe acceleration, the current, and the depth of focus of an electronbeam, by avoiding unnecessary automatic adjustment, and thediversification of a measurement target, improvement in usability of auser, and high-precision measurement can be realized together.

Example 1

FIG. 1 is a diagram showing an outline of a charged particle beam deviceand is for illustrating the configuration of a CD-SEM.

A column 1 of the CD-SEM is provided with an electron gun 2, and a wafer11 disposed on a stage 12 is irradiated with an electron beam 4 emittedfrom the electron gun 2. The inside of the column 1 is evacuated in avacuum state, and the electron beam 4 passes through a vacuum space. Theelectron beam 4 performs one-dimensional or two-dimensional scanning dueto a deflector 5, and electrons which are emitted from the wafer 11 onthe basis of the scanning, or secondary electrons 13 which are generateddue to the electrons colliding with another member are detected by adetector 13. A detection signal 15 is stored in a memory or the likebuilt into a control PC 21 or the like in synchronization with ascanning signal 8 of the deflector 7 and becomes a waveform signal or animage signal.

The control PC 21 (a control device) is provided with a memory in whichan operation program for operating the CD-SEM, which is referred to as arecipe, is stored, and an optical element or a stage built into theCD-SEM is operated according to the recipe. An acceleration voltagecondition of the electron beam according to a measurement target, or afocusing condition (an exciting current) of an objective lens 9 when hasbeen set to the acceleration voltage is written in the recipe, and theoptical conditions of the optical element (the objective lens or thelike) according to measurement coordinates or the type of a sample areautomatically set. Further, information about an optical axis adjustmenttiming using an aligner 7 or the like is also written in the recipe, andit is possible to perform optical axis adjustment (beam alignment) asoften as necessary. Further, the optical axis adjustment is performed bydeflecting the beam such that the electron beam 4 passes through theideal optical axis. For example, in a case of performing the opticalaxis adjustment with the objective lens 9 set as the optical element,the deflection condition (an adjustment condition by an adjustmentelement) of the aligner 7 is adjusted such that the movement (parallax)of an image occurring when the excitation condition of the objectivelens is changed becomes zero or becomes close to zero.

The column 1 and the control PC 21 are connected through a bus line 20,and the bus line 20 transmits signals such as a control voltage 2 whichdetermines the acceleration voltage of the electron gun 2, the detectionsignal 15 which is obtained by the detector 14, an aligner signal 6 ofthe aligner 5, the deflection signal 8 of the deflector 7, and a lenscurrent 10 of the objective lens 9, from the control PC 21 to the column1 and from the control PC 21 to the column 1.

Further, the control PC 21 monitors the lens current 10 in a process inwhich control of moving the stage 12 is performed such that ameasurement point on the wafer 11 is positioned at an irradiation pointof the electron beam 4. A temperature fluctuation 26 due to heatgeneration of the objective lens 9 is found out based on thismonitoring. Further, a temperature threshold value determination 27 isperformed by using a temperature threshold value 24 which chargesaccording to a change of the control voltage 3 (acceleration voltage),and automatic adjustment selection 28 is performed in accordance withthe situation of the device, and automatic adjustment is carried out bycontrolling the optical element by the aligner signal 6, the lenscurrent, or the like.

The temperature threshold value determination 27 is operated accordingto the setting of an automatic adjustment monitor of a recipe editingscreen 25 which is displayed on a GUI 22, and performs a threshold valuedetermination which depends on a measurement target pattern. Theautomatic adjustment selection 28 is operated according to the parametersetting of an automatic adjustment range of the measurement recipeediting screen 25 which is displayed on the GUI 22. A heat generationtemperature log 23 is displayed at the time of the maintenance of thetemperature threshold value 24 or the tuning work of the recipe editingscreen 25. As a result, it becomes possible to perform the automaticadjustment only in a switching condition in which length measurementvalue fluctuation occurs, without a stabilization wait at the time ofthe switching between the optical conditions, and thus the CD-SEM can berealized which enables automatic measurement in which both of high rateof automation due to automatic adjustment at a proper timing and highthroughput due to the avoidance of unnecessary automatic adjustment canbe achieved.

A specific operation principle will be described below. If a constantcurrent is made to flow through a coil of the objective lens over asufficient period of time, the thermal conduction of a constituentmaterial, the thermal conduction of the air, and the amount of heatgeneration are balanced, and thus a temperature enters an equilibriumstate. An equilibrium state due to the heat generation of the objectivelens by an expression of thermal conduction at this time is expressed bythe following expression.ΔT=T−T _(B) =K×Ω×I ² =K×W

T is a temperature, T_(B) is the temperature of the environment in whichthe objective lens is installed, K is an effective thermal resistivity,W is the amount of heat generation, Ω is the resistance of the objectivelens coil, and I is an objective lens current. On the other hand, thedeviation from the equilibrium temperature when the amount of heatgeneration is changed is expressed by the following expressions.

${\delta\; T} = {\left. {\sum_{i}{\frac{\partial T}{\partial t}{dt}}} \middle| {}_{i}{{- K} \times W} \right. = {{\sum_{i}{\frac{1}{\tau}{x\left( {{K \times W_{i}} - {\Delta\; T_{i - 1}}} \right)} \times e^{{- {({t_{i} - t_{i - 1}})}}/\tau}}} - {K \times W}}}$$\mspace{79mu}{{\Delta\; T_{i - 1}} = {\sum_{j = 1}^{i - 1}{\frac{1}{\tau}{x\left( {{K \times W_{j}} - {\Delta\; T_{j - 1}}} \right)} \times e^{{- {({t_{j} - t_{j - 1}})}}/\tau}}}}$

Here, δT is the deviation from the equilibrium temperature of theobjective lens, K is the effective thermal resistivity, τ is arelaxation time, W is the amount of heat generation, and t is a time.From these expressions, if the objective lens starts the monitoring ofthe amount of heat generation from the state of the equilibriumtemperature, thereby tracking setting history, the expression,T_(o)=K×Ω×I₂, is established, and thus it is possible to track ΔT. Evenin a case where ΔT_(o) is not accurate, if the amount of heat generationis monitored for a sufficiently longer period of time than therelaxation time, the influence on the calculation of ΔT can besuppressed. In a case where a time interval to monitor the amount ofheat generation is sufficiently shorter than the relaxation time τ, thedeviation from the equilibrium temperature is expressed by the followingexpressions.

${\Delta\; T_{i}} = {{{\frac{1}{\tau} \times \left( {{K \times W_{i}} - {\Delta\; T_{i - 1}}} \right) \times \left( {t_{i} - t_{i - 1}} \right)} + \tau + {\Delta\; T_{i - 1}\delta\; T}} = {{\Delta\; T_{i}} - {K \times W_{i}}}}$

If a flow of obtaining ΔTi from ΔT_(i−1) and t_(i−1) stored in a memoryby monitoring Wi and ti and calculating them before one time isrepeated, it is possible to accurately determine δT.

FIG. 2 is a flowchart of temperature fluctuation tracking by specificobjective lens setting. A determination of necessity of objective lenstemperature monitoring 202 is performed with a time interval, the amountof current change of the objective lens, or the like as a criterion fordetermination, and in a case where the monitoring is required, δT andΔTi are determined in calculation of deviation from the equilibriumtemperature 203 and held in the device, a temperature fluctuationtracking continuation determination 204 is performed, and the routinereturns back to START 201. Next, in a case where the calculation ofdeviation from the equilibrium temperature 203 is performed, δT andΔT_(i+1) are determined and held in the device.

In a case where the automatic adjustment is carried out due to δTexceeding a threshold value after the setting condition of the electronbeam is changed, δT often exceeds the threshold value at the time of thenext necessity determination. However, in the setting condition of theelectron beam automatically adjusted in a non-equilibrium state, unlikethe setting condition in the equilibrium state of the objective lens, awrong threshold value determination in which automatic adjustment is notessential in the necessity determination is often performed. As aresult, after the setting condition of the electron beam is changed,automatic adjustment is inappropriately carried out in succession. Inorder to avoid this problem, the elapsed time from the previousautomatic adjustment and the temperature fluctuation amount must bechanged to the criteria for the determination of necessity of theautomatic adjustment.

FIG. 3 is a flowchart of a threshold value determination during theautomatic measurement. START 301 is performed in a state where thetemperature fluctuation tracking of FIG. 2 is started in advance andthus δT can be immediately referred, the recipe is read by loading awafer and the setting of the electron beam is made. A threshold valuedetermination 302 is performed due to the deviation from the equilibriumtemperature of the objective lens. Automatic adjustment 303 isperformed, and δT at that time and an implementation time are held inthe device. Measurement after movement to a measurement point 304 isperformed.

In a case where the measurement is continued in 305, the routine returnsback to START 301, and in a case where the setting of the electron beamis changed, the threshold value determination 302 is performed due tothe deviation from the equilibrium temperature of the objective lens,and in a case where the setting of the electron beam is not changed, thethreshold value determination 302 is performed with respect to eachdifference between δT and the implementation time recorded in theprevious automatic adjustment 303. The threshold value determination 302complies with the temperature threshold value with respect to theelectron beam setting, and the recipe setting. The number of measurementpoints when performing the measurement after movement to a measurementpoint 304 complies with the recipe setting.

In general, the setting condition of the electron beam is adjusted bythe optical element in the equilibrium state, and therefore, if thefeature amount of the optical element deviates from the reference value,the focus, the astigmatism, and the axis of the electron beam areshifted. The amount of shift of the focus, the astigmatism, and the axisof the electron beam depends on the acceleration, the current, and thedepth of focus of the electron beam, and therefore, a list of thethreshold values of the feature amount of the optical element needs tobe held in the device. FIG. 4 is an example of a list of temperaturethreshold values with respect to the acceleration, the current, and thedepth of focus of the electron beam. The combination of theacceleration, the current, and the depth of focus depends on the type ofthe device, and there is a case where the combination varies between thedevices. The threshold value is an allowable value of the deviation fromthe equilibrium temperature of the objective lens. There is also a casewhere the threshold value is specified in the range of the referencevalue. In a case where there are a plurality of feature amounts of theoptical element which is monitored, if a list of the threshold values isprovided for each of the feature amounts and can be displayed on theGUI, the list is used at the time of maintenance of the device or recipetuning.

In a semiconductor device mass-production plant, 50 to 2000 pieces oflength measurement recipes per day are input to a single device. A casewhere the threshold value of the feature amount of the optical elementalso depends on a measurement target pattern is also included in thelength measurement recipe. This is because there is a case whereallowable errors of the focus, the astigmatism, and the axis of theelectron beam depend on the measurement target pattern. At this time,unlike the threshold value of the feature amount of the optical elementwhich depends on the acceleration, the current, and the depth of focusof the electron beam, the setting of the threshold value determinationis required for each length measurement recipe which becomes a target.

In FIGS. 5A-5E, five examples of the length measurement recipe editingscreen in which the setting of the threshold value determination duringthe automatic measurement can be made are taken. FIG. 5A is an exampleof the length measurement recipe editing screen which includes only anON/OFF button of the threshold value determination during the automaticmeasurement. FIG. 5B is an example of the editing screen made so as tobe able to set the range of the automatic adjustment for each lengthmeasurement sequence. FIG. 5C is an example of the editing screen in acase where the automatic adjustment is forcibly carried out. FIG. 5D isan example in which change setting of the threshold value determinationis added to the length measurement recipe editing screen in accordancewith the measurement target pattern. FIG. 5E is an example of athreshold value list editing screen for changing the threshold valuedetermination according to the setting history of the electron beam.

There is a case where the tuning of the determination of the thresholdvalue of the length measurement recipe, the maintenance of the list ofthe threshold values of the feature amount of the optical element, orthe like is required. However, the combination of the switchingconditions is a factorial of the setting condition of the electron beamthat the device holds, and the tuning or the maintenance in an actualmachine is difficult. Therefore, the work procedure of the device duringefficient operation, such as a method of confirming the accuracy of thethreshold value determination and a tuning and maintenance method, isdescribed in a manual. In order to proceed with the work in accordancewith the manual, a log screen of the deviation from the equilibriumstate of the feature amount of the optical element of FIGS. 6A-6C isdisplayed and the explanation of the log screen is also described in themanual. FIGS. 6A-6C show examples of the log screen of the deviationfrom the equilibrium state of the feature amount of the optical element.Shown is an example in which automatic adjustment markers 604 areplotted in a log screen of a time axis 601 and a δT axis 602 of thedeviation from the equilibrium temperature of the objective lens. Shownare examples in which logs are shown in the coordinates of a δT axis 606and a length measurement reproducibility 3σ axis 607 with respect to atime axis 605. Instead of the 3σ axis 607, an axis of a lengthmeasurement value, resolution, a focus value, or the like may beadopted.

Due to the miniaturization and complexity of the measurement targetpattern, it is necessary to perform measurement with the setting of theelectron beam changed for each sample type. Especially, in recent years,in addition to an electron beam in a relatively low energy range such asa range of 500 V to 1600 V, an electron beam in a range of 2000 V to5000 V has also been used. However, if the acceleration energy of anelectron beam is greatly changed, the focus of the electron beam isshifted for a long period of time, and astigmatism or axis shift alsooccurs. There is a possibility that the focus shift and the like maybecome a factor of the length measurement value fluctuation. In a casewhere the optical condition is switched at a level in which the lengthmeasurement value fluctuation occurs, it is possible to suppress thelength measurement value fluctuation by providing a waiting time untilthe device is stabilized. However, in a mass-production plant for asemiconductor device or the like, in which higher throughput isrequired, it is believed that improvement of the operating time of thedevice is required.

On the other hand, if an automatic adjustment function such as focusadjustment, astigmatism correction, and axis adjustment of the electronbeam is used, it is possible to suppress the length measurementfluctuation without a waiting time. However, a corresponding time isrequired even for the adjustment, and therefore, it is believed that anautomatic measurement algorithm in which these adjustments are notperformed as much as possible while satisfying a proper opticalcondition is required.

The length measurement value varies according to environment such as anair temperature or air pressure, or a change in the setting of theoptical element in the column. In particular, the length measurementvalue varies according to fluctuation of the amount of heat generationat the time of the switching between the optical conditions of theobjective lens. FIG. 7 is a diagram showing an example of a sequence ofswitching between the optical conditions during the automaticmeasurement. A function of monitoring the fluctuation history of theamount of heat generation of the objective lens, a list of the thresholdvalues of the fluctuation history for each optical condition, a functionof carrying out the automatic adjustment in a case of exceeding thethreshold value, and an exclusive processing function of continuoustriggering occurring in a case of exceeding the threshold value, and theautomatic adjustment with respect to the length measurement sequence areinstalled in the CD-SEM, whereby even in a case where the opticalcondition is greatly changed due to the switching between samples, itbecomes possible to perform high-precision measurement without a waitingtime.

FIG. 9 is a flowchart showing a measurement processing step whenexecuting the measurement of a semiconductor wafer on the basis of anoperation program stored in the recipe, and shows in particular a stepof performing the calculation of the deviation from the equilibriumtemperature of the objective lens, and the calculation of the elapsedtime from the previous automatic adjustment time and the differencebetween an objective lens temperature at the time of the previousautomatic adjustment and the current objective lens temperature, inparallel with the measurement processing. First, the control PC 21 readsthe recipe selected or generated according to a measurement targetsample and sets it to the device as an operation program (Step 901).Next, the wafer 11 is introduced into a sample chamber (not shown) andplaced on the stage 12 (Step 902). Before a sample is placed on thestage, processing for placing the wafer at a proper position on thestage, such as pre-alignment, is executed.

Next, whether or not it is necessary to greatly change the opticalcondition (for example, the excitation condition of the objective lens)is determined with reference to the recipe, and in a case where thechange is required, the setting of the optical condition is performedand a setting time (a counting time) thereof is recorded (Step 903). Thecounting time is used in order to calculate the above-described δT orthe like. Further, in a case where it is not necessary to change theoptical condition, the movement of the stage is performed such that themeasurement point and the irradiation position of the beam coincide witheach other (Step 906). A case where it is necessary to greatly changethe optical condition is, for example, a case of changing theacceleration energy of the electron beam from 500 eV to 5000 eV, and acase of greatly changing the focusing condition of the objective lensaccording to a large change of the acceleration energy correspondsthereto.

When the optical condition is changed at Step 903, a determination ofwhether or not the automatic adjustment such as axis adjustment isexecuted is performed (Step 904). First, the necessity of the automaticadjustment is determined based on a first criterion for determination(Th1). Specifically, in a case where the elapsed time ΔTp from theprevious automatic adjustment time is greater than or equal to apredetermined value (Th11≤ΔTp), the automatic adjustment is executed.The reason to perform such a determination is because it is believedthat after a considerable time has elapsed from the previous automaticadjustment, the optical axis is greatly shifted. Further, in a casewhere a variation between a lens temperature to at the time of theprevious automatic adjustment and the current lens temperature tn isgreater than or equal to a predetermined value (Th12≤(ta−tn)), theautomatic adjustment is executed (Step 905). In Step 905, a countingtime for calculating the above ΔTp is registered.

In a case where a change in the temperature of the lens is greater thanor equal to a predetermined value, it is considered that the objectivelens condition greatly varies in order to approach the equilibriumstate, and there is a case where the condition of the optical axis orthe like changes accordingly, and therefore, the necessity of theautomatic adjustment is determined based on such a criterion fordetermination. Further, in a case where the above-described δT isgreater than or equal to a predetermined value (Th13≤δT), adetermination is made to perform the automatic adjustment. A state whereδT is large is a state where fluctuation over time of the lens conditionis large, and therefore, the state is determined as a timing forperforming the automatic adjustment. In Step 903, a threshold valuedetermination is performed with respect to each of three parameters, andwhen at least one of the three parameters satisfies the abovepredetermined condition, the automatic adjustment is executed. δT is anindex value indicating the deviation of the temperature which is onefeature amount indicating the state of the objective lens. That is, itindicates the difference between the current temperature (a firstfeature amount) and a reaching temperature (a second feature amount)when has entered the equilibrium state, and the objective lens ischanged from a first state to a second state by obtaining such an indexvalue and performing the threshold value determination, and in a case ofimmediately retuning back to the first state, it becomes possible tocontinue measurement without performing unnecessary automaticadjustment.

As described above, by performing the determination of the necessity ofthe automatic adjustment by using the extent of the discrepancy betweenthe automatic adjustment time and the current time, or objective lenstemperature information (the extent of the deviation from theequilibrium temperature, information about the difference between thetemperature of the objective lens at the time of the previous adjustmentand the current objective lens temperature, or the like) which isobtained from the optical condition (an excitation current) of theoptical element such as the objective lens and the elapsed time, itbecomes possible to perform the adjustment at a proper timing.

After the automatic adjustment is performed in Step 905, stage movementis performed such that the irradiation position of the electron beam ispositioned at the measurement target pattern (Step 906). Further, in theflowchart illustrated in FIG. 9, an example in which the automaticadjustment is performed before measurement point movement is described.However, image acquisition in a case of performing the automaticadjustment may be performed at the measurement point. Next, in Step 907,a second threshold value (Th2) determination is performed (Step 907).Here, in a case where the elapsed time from the previous automaticadjustment time is greater than or equal to a predetermined value(Th21≤Tp), or a case where the discrepancy between the lens temperatureat the time of the previous automatic adjustment and the current lenstemperature is greater than or equal to a predetermined value(Th22≤ta−tn), or in a case where any condition is satisfied, adetermination of the automatic adjustment (Step 908) is performed.

At a timing just after the optical condition is changed and theautomatic adjustment based on the first threshold value determination isperformed, the threshold value determination condition using Th21 andTh22 is not satisfied. However, if measurement is continued for a whilewithout changing the optical condition, there is a possibility that axisshift or the like which occurs according to a temporal change or thetransition to the equilibrium state of the objective lens may beactualized, and therefore, by performing the determination of thenecessity of the automatic adjustment as in Step 907, it becomespossible to perform the automatic adjustment at a proper timing.

By passing through the steps as described above, it is possible to knowa proper timing of the automatic adjustment without acquiring an image,and thus it becomes possible to execute image acquisition and themeasurement based on the acquired image, under the proper opticalcondition (Steps 909 and 910). After the measurement of a certainmeasurement point is executed, in a case where there is a measuringpoint which is not measured, the necessity of the automatic adjustmentis determined again and the measurement is then continued. If themeasurement of all the measurement points of the wafer introduced intothe sample chamber is ended, the wafer is carried out of the samplechamber and the measurement of the wafer is ended (Step 911).

In this example, apart from the image acquisition of the SEM, thetemperature state of the optical element such as the objective lens iscontinuously monitored, and therefore, it is possible to perform theautomatic adjustment at a proper timing without performing a wrongdetermination or the like using an image acquired in a state where theoptical condition is shifted.

Example 2

In Example 2, an application example to a review device and aninspection device will be described. A technique of forming a finepattern of a semiconductor device, a liquid crystal device, a hard disk,or the like is composed of processes of a very large number of steps, inwhich the number of processes is up to several hundreds. If defectsoccur in a fine patter or a formed film due to the failure of a process,there is a case where manufacturing defects of a device are generated ina large numbers, and thus, for maintenance and improvement of deviceproduction yield, it is necessary to continuously specify a cause of adefect and carry out a countermeasure. For this reason, defects of thedevice are monitored by inspecting foreign matter, disconnection of awire, or the like for each major process. In general, in an inspectiondevice, an optical application device for foreign material inspection,appearance inspection, or the like is used. However, there is athroughput restriction. For this reason, defects are monitored bymonitoring the number or density of defects by using the narrowing of aprocess range with respect to an inspection target, or snap inspection.Further, there is a case of performing the analysis and classificationof the defect by using a review device of the defect coordinatesdetected by the inspection device. Especially in a review device using ascanning electron microscope, the analysis of a high-magnificationobservation image and an element of the defect is performed.

FIG. 8 is a schematic diagram showing an overall configuration diagramof a charged particle beam device according to the second example, thatis, a review device. The review device is configured of a stage 802 forholding a wafer 801, a column 804 for converging an electron beam 803onto the wafer, a secondary electron detector 807 for convertingsecondary electrons 805 which are emitted from the wafer 801 into adetection signal 806, an image generation system for converting thedetection signal into a digital image, an image processing system foranalyzing the coordinates and the shape feature amount of an observationtarget from the digital image, a deflection signal 808 for irradiatingthe coordinates of the observation target with the electron beam, and adeflector 809 for deflecting the electron beam according to thedeflection signal. If an X-ray detector 811 for converting the X-rayswhich are emitted from the wafer into a characteristic X-ray signal 810is added, a defect can be analyzed in more detail. The automaticadjustment is carried out by holding temperature fluctuation due to heatgeneration 826 by monitoring an objective lens current 812 duringautomatic defect review, performing a temperature threshold valuedetermination 827 by using a temperature threshold value 824 for thesetting of the electron beam which is changed by control voltage 813 orthe like, and controlling an optical element such as an aligner 815 oran objective lens 816 by an aligner signal 814, a lens current, or thelike by performing automatic adjustment selection 828 in accordance withthe situation of the device. The temperature threshold valuedetermination 827 is operated according to the setting of an automaticadjustment monitor of a recipe editing screen 825 which is displayed ona GUI 822, and performs a threshold value determination that depends ona defect review target pattern. The automatic adjustment selection 828is operated according to parameter setting of an automatic adjustmentrange of the inspection recipe editing screen which is displayed on theGUI. A heat generation temperature log 823 is displayed at the time ofthe maintenance of the temperature threshold value 824 or the tuningwork of the inspection recipe editing screen. As a result, it becomespossible to carry out the automatic adjustment only in the switchingcondition in which length measurement value fluctuation occurs, withoutstabilization wait at the time of the switching between the opticalconditions, and thus it is possible to realize the review device whichenables automatic defect review in which both of a high rate ofautomation by the automatic adjustment at a proper timing and highthroughput by avoidance of unnecessary automatic adjustment can beachieved.

A sequence at the time of the switching between the optical conditionsduring the automatic inspection will be described using FIG. 7 again.First, a semiconductor wafer is loaded. Next, inspection data detectedby a foreign matter inspection device and an appearance inspectiondevice is read into a central control device. Next, a target defect isextracted from the inspection data. Next, the column is set so as to beable to be observed in any beam acceleration. Next, wafer alignment isperformed for coordinate correction by using a scanning observationimage or the like of the electron beam. Next, movement to a defectposition is performed by the combination of stage control and deflectionof the electron beam. Next, scanning by the electron beam is performed,and an electric signal which is output from the secondary electrondetector is converted by the image generation system, thereby forming adigital image. Next, the image processing system extracts thecoordinates and the shape feature amount of the target defect from thedigital image. When forming the digital image, there is also a method inwhich the coordinates of the target defect is detected atlow-magnification imaging in advance and a zoom image of the targetdefect is acquired. The shape feature amount is a parameter which isused in order to perform appearance classification of the target defect.Next, the defect coordinates extracted from the digital image areirradiated with the electron beam by using a deflection system. Next,the composition classification of the target defect is performed byacquiring an X-ray energy spectrum which is emitted from the sample. Byrepeating the above flow, it is possible to automatically move to aplurality of target defects and efficiently collect a digital image, ashape feature amount, an element list, or the like for each targetdefect.

Due to the miniaturization and complexity of a defect review targetpattern, it is necessary to change the setting of the electron beam foreach sample type. Due to fluctuation of the focus, the astigmatism, andthe axis of the electron beam, degradation of the image quality of thedigital image, or erroneous detection of the shape feature amount or theelement list occurs during a period of two hours at the maximum fromimmediately after the setting change of the electron beam. In general,in the case of sample replacement according to the setting change of theelectron beam in which the image quality degradation or the erroneousdetection occurs, a waiting time is provided until the device isstabilized. However, in a mass-production plant, it is not possible towait until the device is stabilized, and thus it is required to performdefect review without providing a waiting time for each sample type.

If a function of automatically adjusting the focus, the astigmatism, andthe axis of the electron beam is used, the defect review can becontinuously performed without a waiting time. However, there is a casewhere an adjustment time longer than the defect review time is required.That is, it is problematic that it is not possible to carry out theautomatic adjustment function by extracting the condition in which theimage quality deterioration or the erroneous detection occurs. Thecondition in which the image quality deterioration or the erroneousdetection occurs depends on fluctuation of environment such as an airtemperature and air pressure and the setting history of the column.However, the influence of the fluctuation history of the amount of heatgeneration at the time of the switching between the optical conditionsof the objective lens is strong. Therefore, a function of monitoring thefluctuation history of the amount of heat generation of the objectivelens, a list of the threshold value of the fluctuation history for eachoptical condition, a function of carrying out the automatic adjustmentin a case of exceeding the threshold value, and exclusive processing ofthe automatic adjustment with respect to continuous triggering whichoccurs in a case of exceeding the threshold value, and a lengthmeasurement sequence are installed in the review device, whereby itbecomes possible to continue the defect review without providing awaiting time for each sample type.

REFERENCE SIGNS LIST

-   -   1: column    -   2: electron gun    -   3: control voltage    -   4: electron beam    -   5: aligner    -   6: aligner signal    -   7: deflector    -   8: deflection signal    -   9: objective lens    -   10: objective lens current    -   11: wafer    -   12: stage    -   13: secondary electron    -   14: detector    -   15: detection signal    -   20: bus line    -   21: control PC    -   22: GUI    -   23: heat generation temperature log    -   24: temperature threshold value    -   25: recipe editing screen    -   26: temperature fluctuation due to heat generation    -   27: temperature threshold value determination    -   28: automatic adjustment selection    -   201: START    -   202: determination of necessity of objective lens temperature        monitoring    -   203: calculation of deviation from equilibrium temperature    -   204: temperature fluctuation tracking continuation determination    -   205: END    -   301: START    -   302: threshold value determination    -   303: automatic adjustment    -   304: measurement after movement to measurement point    -   305: measurement continuation determination    -   306: END    -   601: time axis    -   602: δT axis    -   603: log curve of δT    -   604: automatic adjustment marker    -   605: time axis    -   606: δT axis    -   607: 3σ axis    -   801: wafer    -   802: stage    -   803: electron beam    -   804: column    -   805: secondary electron    -   806: detection signal    -   807: secondary electron detector    -   808: deflection signal    -   809: deflector    -   810: characteristic X-ray signal    -   811: X-ray detector    -   812: objective lens current    -   813: control voltage    -   814: aligner signal    -   815: aligner    -   816: objective lens    -   821: control PC    -   822: GUI    -   823: heat generation temperature log    -   824: temperature threshold value    -   825: recipe editing screen    -   826: temperature fluctuation due to heat generation    -   827: temperature threshold value determination    -   828: automatic adjustment flow selection

The invention claimed is:
 1. A charged particle beam device comprising:an optical element configured to adjust a charged particle beam emittedfrom a charged particle source; an adjustment element configured toadjust the charged particle beam incident on the optical element; and acontrol device configured to control the adjustment element, wherein thecontrol device obtains an extent of deviation from an equilibriumtemperature of the optical element based on a condition setting of theoptical element and executes adjustment with the adjustment element whenthe extent of deviation satisfies a predetermined condition.
 2. Thecharged particle beam device according to claim 1, wherein the controldevice executes the adjustment with the adjustment element based onthreshold determination of the extent of deviation.
 3. The chargedparticle beam device according to claim 1, wherein the control devicerecords date and time and the extent of deviation when the adjustmentwith the adjustment element is executed.
 4. The charged particle beamdevice according to claim 1, wherein the adjustment element isconfigured to adjust an incidence condition of the charged particle beamincident on the optical element.
 5. The charged particle beam deviceaccording to claim 4, wherein the incidence condition is at least one ofan acceleration voltage, an incident current, and a depth of focus ofthe electron beam.
 6. The charged particle beam device according toclaim 4, wherein the control device continuously traces or calculatestemperature fluctuation of the optical element based on the conditionsetting and the incidence condition.
 7. The charged particle beam deviceaccording to claim 6, wherein the control device displays executionresult of the adjustment with the adjustment element together withchorological change of the temperature fluctuation.
 8. The chargedparticle beam device according to claim 7, wherein the control devicedisplays at least one of a length measurement value, resolution, a focusvalue, and length measurement reproducibility together with chorologicalchange of the temperature fluctuation.
 9. The charged particle beamdevice according to claim 1, wherein the control device measures alength of a measurement point based on a length measurement recipe afterexecuting the adjustment with the adjustment element.
 10. The chargedparticle beam device according to claim 1, wherein the control deviceobtains elapsed time from previous adjustment time with the adjustmentelement, and executes the adjustment with the adjustment element in acase where the elapsed time is a predetermined value or more.
 11. Thecharged particle beam device according to claim 1, wherein the opticalelement is an objective lens.
 12. The charged particle beam deviceaccording to claim 1, wherein the optical element is an element whichperforms at least one of focus adjustment, astigmatism correction, andaxis adjustment of the electron beam.